Thanks for the good question.
wish to see more like this.
(I guess this depends on the initial type of the data which in the first position.
For this "select '130'+'120'+1" it will give you 130121, but for this "select 1+'120'+'130'" it will give you 251 not 121130. It takes the next value and it converts to the first value's data-type and then so on...
select 0 + '130'+'120'+1 - this gives 251 (because the initial value type is number and it works for only int type)
select 0 + '130'+'120'+2.56 - and the decimal works only with the end value.)
The first and the hardest SQL statement I have wrote- "select * from customers" - and I was happy and felt smart.